First off, if you've been on reddit for more than five minutes you aren't learning a new word. We've heard it. Second, when people call someone a "pedophile" in these situations they are trying to get across that the person is being predatory. The word doesn't do that. In terms of diagnosis, some attraction to 15-19 year olds is considered normal. Ehebophilia is not even a diagnosis in and of itself. It's only considered a problem if it interferes with your life, and even then the diagnosis is "Paraphilia NOS."

Consequently, "ehebophile" comes off as both apologetic and soft-pedalling. It does not, at all, express the thing people are disturbed about - the predatory nature of the relationship. Since there is no term for "someone who is predatory in their attraction to people who are 15-19," people go with "pedophile" because that's the term that gets the awful part across.

Additionally, people see it as downplaying the problem through nitpicking. There's technically a difference, but since the point is "he is being predatory to a very young person" and not "he is neutrally sometimes attracted to people who may have been legal for years," it's a difference that doesn't matter here.

Finally, we're here to help someone whose brother is being preyed upon, not clear our throats and say "Yes, well, but it'd be a worse crime if he was five." That's a shitty thing to say to someone whose little brother is in trouble, and a shitty thing to take away as the important part. How helpful is it, really, to make sure she knows that her that her brother is being fed pills by a rapist who technically isn't a pedophile?

Actually finally, "ehebophilia" champions should really think about if they want it to take on the colloquial sense of being innately predatory, because that's all this little dance is doing. I mean, I think it should, I just find it so funny that this "well, TECHNICALLY" gambit for normalization is backfiring so hard.